1. Field of the Invention
The present invention relates to an electrochemical cell that includes a stacked or folded arrangement of electrode plates, and U-shaped current collectors disposed in the cell that form an electrical connection with the electrode plates, and cooperate to retain the electrode plates in a desired configuration.
2. Description of the Related Art
Battery packs provide power for various technologies ranging from portable electronics to renewable power systems and environmentally friendly vehicles. For example, hybrid electric vehicles use a battery pack and an electric motor in conjunction with a combustion engine to increase fuel efficiency. Battery packs are formed of a plurality of electrochemical cells. The cells are arranged in two or three dimensional arrays and are electrically connected in series or in parallel.
Different cell types have emerged in order to deal with the space requirements of a very wide variety of installation situations, and the most common types used in vehicles are cylindrical cells, prismatic cells, and pouch cells. Regardless of cell type, each cell includes an electrode assembly that is sealed within a cell housing along with an electrolyte to form a power generation and storage unit. The electrode assembly may include an alternating arrangement of positive and negative electrode elements separated by intermediate separator plates, and can be provided in various configurations, including a stacked arrangement of individual electrode sheets, an elongated electrode pair that is wound into a jelly-roll arrangement, or an elongated electrode pair that is z-folded to form a stacked arrangement.
The energy production volumetric efficiency of the cell, as determined by the ratio of (the volume of the electrode assembly disposed within the cell) to (the volume of the cell housing), is relatively low. For example, some cylindrical cells having a jelly-roll electrode assembly may be 80 to 90 percent volumetrically efficient, and some prismatic cells having a jelly-roll electrode assembly may be 60-75 percent volumetrically efficient. Traditionally, a prismatic or pouch type cell having a stacked arrangement of individual electrode plates can be more volumetrically efficient than one having a jelly-roll arrangement, but manufacture of the stacked arrangement is more difficult and prone to mistakes and thus more expensive than that of the jelly roll arrangement. In addition, in some pouch cells, a stack band that surrounds the stacked or folded arrangement of electrodes is used to retain the electrodes in the desired stacked and aligned configuration. In addition to the stack band, such pouch cells also include current collectors disposed in the cell housing that provide an electrical connection between electrode elements of a given polarity and a corresponding terminal. It is desirable to increase the energy production volumetric efficiency of the cell while reducing the complexity of the cell constituents.